Water soluble rapid prototyping support and mold material

ABSTRACT

Formation of polymeric prototype elements is effected by high pressure and high temperature extrusion of selected materials onto a plate as a ribbon of liquefied polymer comprising poly(2-ethyl-2-oxazoline) and a polar polymer discharged in a programmed pattern.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This is a divisional of U.S. application Ser. No.09/096,100,filed Jun. 11, 1998; which is a continuation in part of U.S. applicationSer. No. 09/082,064, filed May 20, 1998, now U.S. Pat. No. 6,070,107;which is a continuation in part of U.S. application Ser. No. 08/825,893,filed Apr. 2,1997, now U.S. Pat. No. 6,067,480; all of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to thermoplastic polymer materials for thepreparation of three-dimensional prototypes or models. Prototypes ofparts are made and used in testing in a wide-variety of industries, suchas the automobile, aerospace, and biomedical prostheses manufacturingindustries. After successful testing the prototypes of parts, a mold ofthe prototype can be made and the part can be manufactured on a massproduction basis.

[0003] There are three ways of making prototypes. One method involvessimply making a mold of the part, making the prototype, and then testingthe prototype. However, this method requires the cost of making a mold,which itself can be extremely expensive and time-consuming. Moreover,this method may require numerous molds to be made on a trial and errorbasis until a successful part has been designed that sufficiently passesthe required testing.

[0004] A second method of making prototypes involves sculpting athree-dimensional prototype of a particular shape from a block workpiece. In this method, the prototype is drawn either manually or usingcomputer-aided design (CAD) techniques, and the prototype is formed byremoving material from a block work piece. The part can be furthermachined either manually or using computer-aided machining (CAM)techniques. However, this method can also be a costly and time-consumingprocess because it may require repeated iterations until a desiredprototype is made.

[0005] A third method that has been developed involves the formation ofa three-dimensional prototype by depositing multiple layers of amaterial in a fluid state onto a base. The fluid solidifies to definethe prototype element. In general this method is often termedfreeforming in the prior art. For example, such a method is taught inU.S. Pat. No. 5,340,433, and U.S. Pat. No. 5,121,329, both issued to S.Scott Crump and assigned to Stratasys, Inc. incorporated herewith byreference. In this method, a layer of the fluid material solidifies andthen another layer of fluid material is deposited over the precedinglayer. The thickness of each layer is controlled by the distance betweenthe tip of the dispensing head and the preceding layer. However, thereare a number of disadvantages to the method and apparatus taught in thisthird method because only certain types of materials can be suitablyused to make the prototypes, such as waxes having low melt viscosity andstrength. Thermoset materials may be used to try to improve strength andtoughness. In any event, this prior art deposition method may notproduce durable prototypes made from high performance engineeringpolymers and composites.

[0006] There is a clear need for a method and apparatus that can makestronger and tougher prototypes made of engineering polymers andcomposites having high melt viscosity and long chain lengths. Such amethod and apparatus is disclosed in U.S. Pat. No. 6,067,480, which isincorporated herein by reference.

[0007] As noted in U.S. Pat. No. 6,067,480, materials for high pressurefused deposition include polyaryletherketone (PEEK® produced byVictrex), polmethylmethacrylate (PMMA® produced by DuPont),polycarbonate (Lexan® made by General Electric Plastics), thermoplasticpolyurethane (Pellethane(® made by Dow Chemical), and polylaticacid/polyglycolic acid block copolymer (a bio-absorbable material madeby a Biomet joint venture). Fused deposition of fiber reinforced gradesof engineering polymers and composites, for example PEEK® and Lexan® canalso be used for the invention disclosed in U.S. Ser. No. 08/825,893.Moreover, prototypes can be made in accordance with that invention usingfiber reinforcement. For example, carbon fiber reinforced PEEK®materials had a tensile strength of over 36,000 psi, exhibited a veryhigh fracture toughness and demonstrated highly anisotropic mechanicalproperties whereas unreinforced materials did not.

[0008] Thus, there is a clear need for strong materials that can be usedin a method for making prototypes, and in particular materials for themethod involving the depositing of multiple layers in a fluid state ontoa base. More specifically, there is a need for strong thermoplasticpolymers that can be easily melt extruded by an extrusion freeformingapparatus in layer form, and which then solidify upon cooling so thatcomplicated shaped parts can be freeform fabricated by precisely andsequentially depositing polymer layers upon one another until thedesired component is produced. There is also a need for strong materialsthat can be used as a support material for use in an extrusionfreeforming apparatus that prevents the sagging of deposited molten,prototype material layers before cooling and solidification. Supportmaterials are particularly important when fabricating complex geometry,dimensionally accurate prototypes having numerous overhangs, or internalcavity features.

BRIEF SUMMARY OF THE INVENTION

[0009] In the present invention, a unique thermoplastic polymermaterial, i.e., poly(2-ethyl-2-oxazoline) (referred to hereafter as“PEO”), is used as a polymer layer material as well as a supportmaterial in a freeform fabrication process. More specifically, PEO ismelt extruded by a freeforming apparatus in layer form. The PEO layerssolidify upon cooling and complicated shaped parts can be freeformfabricated by precisely and sequentially depositing polymer layers uponone another until the desired component is produced. Thus, prototypescan be directly free formed by an extrusion freeforming apparatus usingPEO as a raw material.

[0010] In addition, in the present invention, PEO is used as a supportmaterial for use in rapid prototype processes such as extrusion freeformfabrication or a a fused deposition modeling process. In particular,many parts which are fabricated by these processes have complicatedoverhang geometries which require the use of a support material thatprevents the sagging of deposited molten, prototype material layersbefore cooling and solidification.

[0011] It has been discovered that a major advantage of PEO over othermaterials is that PEO is a high strength rigid thermoplastic polymerthat is easily and accurately extruded and has a good slump resistanceat temperatures less than about 200° C. PEO also has the added benefitsin that it is essentially an amorphous polymer that does not undergosignificant shrinkage upon solidification. Polyethylene oxide, anothercommercially available water soluble thermoplastic, on the other hand,undergoes approximately 15-20% shrinkage due to crystallization uponsolidification. Shrinkage on the order of this magnitude puts a greatdeal of stress and may induce warpage in free formed support materiallayers. PEO also has high degree of interlayer adhesion when freeformed. Polyethylene oxide has negligible interlayer adhesion when freeformed. A major benefit of using PEO is that it has all of the aboveproperties coupled with high water solubility. Rapid prototype parts cantherefore be fabricated using PEO as a support material and the PEOsupport can be easily washed away with water from the completedprototype part without employing toxic and environmentally detrimentalsolvents, which may also dissolve the desired polymer prototype part. Itis believed that PEO is the only commercially available non-ionic watersoluble thermoplastic material (sold under the tradename Aquazol byPolymer Chemistry Innovations Inc., of Tucson, Ariz.) that has all ofthe above properties. PEO is also very tacky and many materials readilyadhere to it, thereby making PEO an excellent rapid prototyping supportmaterial.

[0012] Furthermore, PEO is not as hygroscopic compared to othercommercial water soluble polymers including polyvinyl alcohol andpolyethylene oxide, and thus PEO possesses significantly greaterdimensional stability in ambient humid atmosphere compared to theseother polymers. Moreover, PEO can be extruded at higher temperatureswithout decomposing and having its melt viscosity change with time.

[0013] In another aspect of the present invention, PEO is used as afugitive mold material for casting ceramic slurries, e.g. for ceramicgreen body fabrication, and also preparing polyurethane or epoxy partsby pouring reactive mixtures of these liquid precursor materials into amold which is precision machined from bulk PEO stock. Thus, inaccordance with the present invention, parts can be subsequentlyextracted from the mold by placing the entire part in a water bath afterthe slurry or precursors are cured so that the water dissolves the PEOand leaves the fabricated polymer or green ceramic part behind.

[0014] This unique polymer PEO, not heretofore suggested for use asanextrusion freeform fabrication material, greatly facilitates theextrusion free form fabrication of parts, as well as for casting ceramicslurries.

[0015] These and other objects, advantages and features of the presentinvention will be more fully understood and appreciated by reference tothe detailed description which follows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] PEO as Cylindrical Feed Rod Material

[0017] In a preferred embodiment of the present invention, the specificthermoplastic polymer material poly(2-ethyl-2-oxazoline), i.e., PEO, wasprepared as a slug in the form of a cylinder having the followingdimensions: 0.3 875 inches in diameter by 5.50 inches in length.

[0018] Thereafter, the slug was inserted into an apparatus, the typedescribed in U.S. Pat. No. 6,067,480 and extruded as a fine ribbon bysaid apparatus to form a prototype mechanical element or object. Morespecifically, the steps performed comprised the steps of:

[0019] a) positioning a cylindrical rod of said polymer materialcomprising PEO in a cylindrical housing having a throughbore with adiameter substantially equal to the diameter of the cylindrical rod,said housing being connected with and attached to a discharge headmember having a uniform diameter bore connecting with the throughbore, adischarge tip, a reduced diameter discharge opening in the tip, and acircumferential heater to liquefy the material in the bore;

[0020] b) compressing the material in the housing with a piston whilesimultaneously liquefying the material in the head member to therebydischarge a ribbon of material from the tip;

[0021] c) transporting the platform in the x and y directions whiledischarging material thereon to form the cross sectional shape of theelement; and

[0022] d) transporting the housing and head member in the z directionsimultaneously to form the element in elevation. The extrusion occurredin multiple layers of a ribbon of the material discharged from thenozzle of the apparatus layer upon layer so as to form the object.

[0023] The polymer material comprising PEO can be used as a support forfree formed layers of other material. Further, the method of the presentinvention can be used to make an article of manufacture that is a freeform three-dimensional object comprising a plurality of layers of aribbon of PEO. The present invention further includes a thermoplasticpolymer in the form of an extrudable object comprising a slug of PEO.

[0024] At least one inorganic filler can be added to the polymermaterial comprising PEO. The inorganic filler can be comprised of atleast one soluble salt. Examples of soluble salts include alkali oralkaline earth halides (e.g., sodium chloride, magnesium chloride) ortheir sulfates (e.g., magnesium sulfate).

[0025] The PEO can be blended with at least one inert filler. The inertfiller can be selected from the polymer filler group consisting ofcalcium carbonate, glass spheres, graphite, carbon black, carbon fiber,glass fiber, talc, wollastonite, mica, alumina, silica and siliconcarbide.

[0026] The typical extrusion temperature of the polymer in the headmember can be in the range of about 120-410° C., and is preferably inthe range of 150-200° C., and most preferably approximately 175° C. Therod is compressed and extruded at a pressure of about 200-1,000 psi, andis preferably compressed and extruded at a pressure in a range of about500-700 psi.

[0027] Tensile test bar specimens were extrusion free-formed inaccordance with ASTM D638 testing standard using both 200,000 and 50,000molecular weight (MW) Aquazol feedrods. These specimens were tested andcompared with objects made using similar apparatus. The various objects,i.e., prototype mechanical elements, were then tested and compared oneto the other and the test results are reported below.

[0028] Mechanical Testing

[0029] Mechanical tests were carried out on polymer resins manufacturedinto test configurations in accordance with the same extrusionfreeforming fabrication process previously referred to above. Sampleswere tensile tested to determine their strengths, moduli and elongationto break values. The polymers tested were the PEO of the presentinvention, ABS and Nylon- 11. The test results are shown in Table Ialong with reported test results of other materials. In addition tomechanical testing, sample tensile properties were measured and comparedto reported properties of the other materials.

[0030] Tensile Testing

[0031] Tensile tests were performed as close to standard ASTM D638 aspossible. Tensile bars were free formed and tested without furthermachining or modification. The test specimen geometry was of the typical“dog bone” shape. Machining the bars resulted in damage to the gaugesection of some materials. Since tensile testing is very sensitive tonotches, machining was not possible.

[0032] Samples were tested along the writing direction. This simplydenotes the bead direction with respect to the mechanical testingequipment. The equipment used was a model 1011 Instron apparatus with aload cell capacity of 1000 pounds. The 1011 Instron apparatus usesvertical specimen loading and wedge-action type grips. The cross headspeed for all specimens was 0.2 inches per minute.

[0033] Tensile moduli strength, 0.2% yield strength, and elongation orstrain to fracture were calculated.

[0034] Discussion of Results

[0035] The values contained in Table I resulted from averaging the testsamples' measured properties of interest.

[0036] The mechanical properties of the materials prepared in this workare compared with other free formed polymer materials in Table I. ThePEO is more than 30 percent stronger and between 2 to 3 times stifferthan any of the presently available water soluble polymer materials.These properties represent a substantial improvement in the art. TABLE 1Comparison of Materials Properties from Commercial SFF Systems σ tensileΕ tensile ε break System Material Grade (psi) (ksi) (%) 3D Epoxy XB51702,400 130 9 DTM Nylon-11 LN4000 5,200 200 32 Stratasys ABS 5,000 360 50ACR PEEK 450 FC 36,374 1195 3 ACR Poly- Union Carbide 3,000 40-70 500ethylene Polyox WSR- oxide N80 (200,000 MW) ACR PEO Aquazol 200 4,000230 1.9 (200,000 MW) ACR PEO Aquazol 50 900 150 0.9  (50,000 MW)

[0037] PEO in Filament Applications

[0038] PEO has been found to be not only useful as cylindrical feed rodmaterial, but also as filament feed material in yet another preferredembodiment of the present invention. It has been discovered that PEO isan excellent filament feed material that can be free formed using fuseddeposition modeling processes taught in U.S. Pat. No. 5,340,433 and U.S.Pat. No. 5,121,329 because it is water soluble and can be washed awayeasily, is a stiff material, is thermally stable, and adheres well toother materials, including other layers of PEO. Therefore, PEO filamentfeedstock can be used as a support material in fused deposition modelingof polymer prototype parts.

[0039] Thus, the present invention includes a method for formingprototype mechanical elements from at least one polymer material on aplatform comprising the steps of:

[0040] a) placing filament containing said polymer material comprisingpoly(2-ethyl-2-oxazoline) in a cylindrical housing having a throughborewith a diameter substantially equal to the diameter of the filament,said housing being connected with and attached to a discharge headmember having a uniform diameter bore connecting with the throughbore, adischarge tip, a reduced diameter discharge opening in the tip, and acircumferential heater to liquefy the material in the bore;

[0041] b) liquefying the material in the head member to therebydischarge a ribbon of material from the tip;

[0042] c) transporting the platform in the x and y directions whiledischarging material thereon to form the cross sectional shape of theelement; and

[0043] d) transporting the housing and head member in the z directionsimultaneously to form the element in elevation.

[0044] The polymer material comprising PEO can be used as a support forfree formed layers of other material. Further, the method of the presentinvention can be used to make an article of manufacture that is a freeform three-dimensional object comprising a plurality of filament layersof PEO. The present invention further includes a thermoplastic polymerin the form of an extrudable object comprising a filament of PEO.

[0045] Further it has now been discovered that PEO can be blended with avariety of polar thermoplastics, fillers, and plasticizers to modify itsphysical properties. These additives enable the PEO polymer to beextruded into tough, flexible geometries (including Stratasys FusedDeposition Modeller (FDM®) filament form).

[0046] The polymer material comprising PEO can also include an inorganicfiller, which in turn can be comprised of at least one soluble salt.

[0047] The PEO can be blended with at least one inert filler. The inertfiller can be selected from the polymer filler group consisting ofcalcium carbonate, glass spheres, graphite, carbon black, carbon fiber,glass fiber, talc, wollastonite, mica, alumina, silica and siliconcarbide.

[0048] The typical extrusion temperature of the polymer in the headmember can be in the range of about 120-410° C., and is preferably inthe range of 150-290° C., and most preferably approximately 180° C.

[0049] As a further example, the modulus of PEO can be decreased by theaddition an alcohol plasticizer. Preferably the alcohol plasticizer isin an amount of 0.5 to 45 wt. % alcohol plasticizer to the PEO.Preferred alcohol plasticizers are water soluble and have structurescomposed of multiple hydroxyl groups (i.e., ethylene glycol, glycerol or200-10,000 MW Union Carbide PEG polyethylene glycols). 600 MW PEG is apreferred plasticizer due to its combination of low viscosity and lowmelting point. These plasticizers decrease the rigidity of PEO andenable it to be drawn into flexible filament feedstock that can beextruded by a Stratasys Fused Deposition Modeller (FDM(®) machine.Furthermore, PEG plasticizers are miscible with water and are believedto enhance the overall water solubility and dissolution rate of the freeformed plasticized PEO material.

[0050] PEG plasticized PEO filament is highly tacky in humid atmosphere,which makes it difficult to uniformly spool as feed material through theStratasys FDM® machine dispensing head. Consequently, its formulationmust be modified to decrease its tackiness as well as enhance itsstrength. Addition of 0.25 -5 wt. % of polar wax has been shown todecrease filament tackiness. The polar wax can be selected from thegroup consisting of compounds having alcohol, acid, ester or amidefunctional groups. Thus, in the present invention it is contemplatedthat among the various compounds that can be used include, but are notlimited to amide waxes, including oleamide and stearamide, stearic acid,and stearate/oleate esters. In particular, an ethoxylated fatty alcoholknown under the tradename of Unithox 420 (Baker Petrolite Corporation,Tulsa, Okla.) has been found to reduce filament tackiness. The structureof Unithox 420 is given below:

CH₃CH₂(CH₂CH₂)_(x)CH₂CH₂(O CH₂CH₂)_(y)OH

[0051] where x/y ranges from 4-10, but the preferred ratio is about 5.2

[0052] Unithox 420 is believed to be uniformly soluble in the PEGplasticized PEO at elevated temperatures but phase separates from themixture and migrates to the extruded filament surface upon cooling. Thisleaves a slightly waxy, low tackiness surface upon the cooled filament.

[0053] Polar homopolymers and copolymers containing polar functionalgroups, either pendant to or present in its main chain, can be added toPEG plasticized PEO formulations in order to increase the strength andtoughness of the filament. Examples of polar homopolymers and copolymersthat can be added to the PEG plasticized poly(2-ethyl-2-oxazoline)include Nylon 12, amorphous nylon copolymer ofterephthalamide/isophthalamide/hexamethylenediamide, Nylon 6/Nylon 12copolymer, polyvinylformal, polyvinylbutyral and polyesters. Thesepolymers also decrease the tendency of the filament to fracture when itis fed through the rollers on the Stratasys FDM® machine head. Examplesof polyamides include Nylon 12 (Grilamid L16) and an amorphous nyloncopolymer of terephthalamide/isophthalamide/hexamethylenediamide(Grivory G16), both manufactured by EMS American Grilon Inc., Sumter,S.C., and Nylon 6/Nylon 12 Copolymer (Vestamelt 430P-1), made byHuls/Creanova Inc., Somerset, N.J. These polyamides can be present inamounts ranging from 0.5-35 wt. % based upon the total mass of PEGplasticized PEO.

[0054] Specific examples of water soluble plasticized PEO compositionsthat can be extruded into flexible filament and successfully extrudedthrough a Stratasys FDM head presented below: EXAMPLE I CalciumCarbonate* 22.3 wt. % PEO (200K MW) 65.0 PEG (600 MW) 8.6 Grilamid LI 64.1 EXAMPLE II Calcium Carbonate* 59.1 PEO (50K MW) 26.9 PEG (600 MW)11.1 Vestamelt 43OP-1 2.9 EXAMPLE III Calcium Carbonate* 26.1 PEO (200KMW) 57.5 PEG (600 MW) 10.-0 Grilamid LI 6 4.9 Unithox 1.5 EXAMPLE IVCalcium Carbonate* 22.4 PEO 50K MW) 60.9 PEG (600 MW) 6.9 Grivory G- 16Nylon 6.7 Unithox 420 3.1 EXAMPLE V CaCO₃ 59.25 PEO (200K MW) 26.25 PEG(600 MW) 10.80 Polyvinylbutyral** 3.70 EXAMPLE VI CaCO₃ 25.98 PEO (200KMW) 58.96 PEG (600 MW) 8.35 Phenoxy PKHM 301*** 3.70 Unithox 420 1.52EXAMPLE VII CaCO₃ 26.09 PEO (200K MW) 59.23 PEG (600 MW) 8.39 Tyril125**** 4.76 Unithox 420 1.53

[0055] Polyvinylbutyral used is known under the tradename Butvar B-98,made by Monsanto Company of St. Louis, Mo.

[0056] Phenoxy PKHM 301 is a linear thermoplastic phenoxy resin oligomerblend obtained from Phenoxy Specialists (Division in InChem Corp.), RockHill, S.C.

[0057] Tyril 125 is a styrene-acrylonitrile (SAN) copolymer manufacturedby Dow Chemical Corp., Midland, Mich. Preferred SAN copolymers have anamount ranging from about 20-40 wt. % acrylonitrile repeat units presentin the polymer chains.

[0058] Examples VI and VII are believed to provide the most preferredembodiments of the present invention in that they are the easiest toformulate, and both exhibit excellent fluidity characteristics. Thus, itis preferred that the polar polymer added to the PEO is a polar polymerselected from the group consisting of compounds having nitrilefunctional groups (like Example VII) or compounds having ether andhydroxyl functional groups (like Example VI). Further, the linearthermoplastic phenoxy resin oligomer blend of Example VI and thestyrene-acrylonitrile copolymer of Example VII each exhibited a highdegree of thermodynamic compatibility with PEO polymers.

[0059] Those of skill in the art will recognize various changes to themethods, materials, component ratios, and apparatus are possible withoutdeparting from the spirit and scope of the invention. Thus, theinvention is to be limited only by the claims and equivalents thereof.

[0060] Although the present invention has been described with referenceto preferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A thermoplastic polymer in the form of an extrudable objectcomprising in combination a filament of poly(2-ethyl-2-oxazoline) and apolar polymer selected from the group consisting of compounds havingnitrile functional groups, compounds having ether and hydroxylfunctional groups, and mixtures thereof.
 2. A thermoplastic compositionsuitable for three-dimensional modeling, comprisingpoly(2-ethyl-2-oxazoline) and a polar polymer selected from the groupconsisting of compounds having nitrile functional groups, compoundshaving ether and hydroxyl functional groups, and mixtures thereof. 3.The thermoplastic composition of claim 2 , wherein the polar polymer isselected from the group consisting of a linear thermoplastic phenoxyoligomer blend and a styrene-acrylonitrile copolymer.
 4. Thethermoplastic composition of claim 2 , and further comprising aplasticizer.
 5. The thermoplastic composition of claim 4 , wherein theplasticizer is a water-soluble alcohol plasticizer.
 6. The thermoplasticcomposition of claim 2 , and further comprising an inert filler.
 7. Thethermoplastic composition of claim 6 wherein the inert filler isselected from the polymer filler group consisting of calcium carbonate,glass spheres, graphite, carbon black, carbon fiber, glass fiber, talc,wollastonite, mica, alumina, silica and silicon carbide.
 8. Thethermoplastic composition of claim 5 , and further comprising an inertfiller.
 9. The thermoplastic composition of claim 8 , wherein the inertfiller is selected from the polymer filler group consisting of calciumcarbonate, glass spheres, graphite, carbon black, carbon fiber, glassfiber, talc, wollastonite, mica, alumina, silica and silicon carbide.10. The thermoplastic composition of claim 2 , in the form of anextrudable object.
 11. The thermoplastic composition of claim 10 ,wherein the extrudable object is a filament.
 12. The thermoplasticcomposition of claim 10 , wherein the extrudable object is a slug.